1. Field of the Invention
The present invention generally relates to communications systems and, more particularly, to those which support half duplex communications.
2. Background of the Invention
At a given time, a half duplex logical channel in a wide area communications system typically will allow only a single subscriber station to communicate media to other subscriber stations associated with the same half duplex logical channel. The subscriber station that is allowed to communicate is generally referred to as a “floor owner.” The process of selecting a floor owner from a plurality of subscriber stations seeking to communicate is generally referred to as “floor control.”
Certain wide area communications systems do not provide a centralized floor control mechanism to assign floor ownership for a given half duplex logical channel. In such systems, the subscriber stations signal their requests for floor ownership by transmitting floor requests directly to other subscriber stations associated with the same half duplex logical channel. Such floor requests can be explicit or implicit. An explicit floor request is a floor request that is distinct from media being communicated, whereas an implicit floor request is coupled to the media.
Each of the subscriber stations that receives such a request typically selects a floor owner by selecting the remote subscriber station that transmitted the floor request which it first receives, assuming floor ownership is not currently assigned, of course. In such an arrangement, it is possible for receiving subscriber stations to receive floor requests from multiple subscriber stations attempting to acquire floor ownership at roughly the same time. Moreover, differing signal propagation delays may exist between the plurality of subscriber stations associated with the same half duplex logical channel. As a result, different subscriber stations may grant floor ownership to different transmitting subscriber stations. Such unsynchronized behavior can disrupt communications amongst a group of subscriber stations associated with the same half duplex logical channel, as individual subscriber stations belonging to the group may be reproducing different data streams concurrently.
In communications systems that do provide a centralized request and grant mechanism, a subscriber station typically requests floor ownership by communicating a request for floor control to a centralized controller. Assuming floor ownership is currently available, the first request for floor control received by the controller for a given half duplex logical channel is typically granted. Later requests from other subscriber stations trying to access that same half duplex logical channel will typically be denied until the selected floor owner gives up floor ownership. Use of a centralized controller adds costs to a communications system, however.